Photovoltaic cell with mesh electrode

ABSTRACT

Photovoltaic cells that have a mesh electrode, as well as related systems, methods and components, are disclosed.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation-in-part of, and claimspriority under 35 U.S.C. §120 to, U.S. patent application Ser. No.10/395,823, filed Mar. 24, 2003, and entitled “Photovoltaic CellsUtilizing Mesh Electrodes,” the entire contents of which are herbyincorporated by reference.

TECHNICAL FIELD

[0002] The invention relates to photovoltaic cells that have a meshelectrode, as well as related systems, methods and components.

BACKGROUND

[0003] Photovoltaic cells are commonly used to transfer energy in theform of light into energy in the form of electricity. A typicalphotovoltaic cell includes a photoactive material disposed between twoelectrodes. Generally, light passes through one or both of theelectrodes to interact with the photoactive material. As a result, theability of one or both of the electrodes to transmit light (e.g., lightat one or more wavelengths absorbed by a photoactive material) can limitthe overall efficiency of a photovoltaic cell. In many photovoltaiccells, a film of semiconductive material (e.g., indium tin oxide) isused to form the electrode(s) through which light passes because,although the semiconductive material may have a lower electricalconductivity than electrically conductive materials, the semiconductivematerial can transmit more light than many electrically conductivematerials.

[0004] There is an increasing interest in the development ofphotovoltaic technology due primarily to a desire to reduce consumptionof and dependency on fossil fuel-based energy sources. Photovoltaictechnology is also viewed by many as being an environmentally friendlyenergy technology. However, for photovoltaic technology to be acommercially feasible energy technology, the material and manufacturingcosts of a photovoltaic system (a system that uses one or morephotovoltaic cells to convert light to electrical energy) should berecoverable over some reasonable time frame. But, in some instances thecosts (e.g., due to materials and/or manufacture) associated withpractically designed photovoltaic systems have restricted theiravailability and use.

SUMMARY

[0005] The invention relates to photovoltaic cells that have a meshelectrode, as well as related systems, methods and components. The meshelectrode is formed of a material that provides good electricalconductivity (typically an electrically conductive material, butsemiconductive materials may also be used), and the mesh electrode hasan open area that is large enough to transmit enough light so that thephotovoltaic cell is relatively efficient at transferring the light toelectrical energy.

[0006] In one aspect, the invention features a photovoltaic cell thatincludes two electrodes and an active layer between the electrodes. Atleast one of the electrodes is in the form of a mesh. The active layerincludes an electron acceptor material and an electron donor material.

[0007] In another aspect, the invention features a system that includesa plurality of photovoltaic cells, with each of the photovoltaic cellsincluding two electrodes and an active layer between the electrodes. Atleast one of the electrodes is in the form of a mesh. The active layerincludes an electron acceptor material and an electron donor material.In some embodiments, two or more of the photovoltaic cells areelectrically connected in parallel. In certain embodiments, two or moreof the photovoltaic cells are electrically connected in series. Incertain embodiments, two or more of the photovoltaic cells areelectrically connected in parallel, and two or more differentphotovoltaic cells are electrically connected in series.

[0008] In a further aspect, the invention features a photovoltaic cellthat includes first and second electrodes, an active layer between thefirst and second electrodes, a hole blocking layer between the firstelectrode and the active layer, and a hole carrier layer between themesh electrode and the active layer. At least one of the electrodes isin the form of a mesh. The active layer includes an electron acceptormaterial and an electron donor material.

[0009] In another aspect, the invention features a system that includesa plurality of photovoltaic cells, with each of the photovoltaic cellsincluding first and second electrodes, an active layer between the firstand second electrodes, a hole blocking layer between the first electrodeand the active layer, and a hole carrier layer between the secondelectrode and the active layer. At least one of the electrodes is in theform of a mesh. The active layer includes an electron acceptor materialand an electron donor material. In some embodiments, two or more of thephotovoltaic cells are electrically connected in parallel. In certainembodiments, two or more of the photovoltaic cells are electricallyconnected in series. In certain embodiments, two or more of thephotovoltaic cells are electrically connected in parallel, and two ormore different photovoltaic cells are electrically connected in series.

[0010] Embodiments can include one or more of the following aspects.

[0011] The mesh electrode can be a cathode or an anode. In someembodiments, a photovoltaic cell has a mesh cathode and a mesh anode.

[0012] The mesh electrode can be formed of wires. The wires can beformed of an electrically conductive material, such as an electricallyconductive metal, an electrically conductive alloy, or an electricallyconductive polymer. The wires can include a coating of an electricallyconductive material (an electrically conductive metal, an electricallyconductive alloy, or an electrically conductive polymer).

[0013] The mesh electrode can be, for example, an expanded mesh or awoven mesh. The mesh can be formed of an electrically conductivematerial (an electrically conductive metal, an electrically conductivealloy, or an electrically conductive polymer). The mesh can include acoating of an electrically conductive material (an electricallyconductive metal, an electrically conductive alloy, or an electricallyconductive polymer).

[0014] The electron acceptor material can be, for example, formed offullerenes, inorganic nanoparticles, discotic liquid crystals, carbonnanorods, inorganic nanorods, oxadiazoles, or polymers containingmoieties capable of accepting electrons or forming stable anions (e.g.,polymers containing CN groups, polymers containing CF₃ groups). In someembodiments, the electron acceptor material is a substituted fullerene.

[0015] The electron donor material can be formed of discotic liquidcrystals, polythiophenes, polyphenylenes, polyphenylvinylenes,polysilanes, polythienylvinylenes and/or polyisothianaphthalenes. Insome embodiments, the electron donor material is poly(3-hexylthiophene).

[0016] A photovoltaic cell can further include a hole blocking layerbetween the active layer and an anode (e.g., a mesh anode or a non-meshanode). The hole blocking layer can be formed of, for example, LiF ormetal oxides.

[0017] A photovoltaic cell can also include a hole carrier layer betweenthe active layer and the cathode (e.g., a mesh cathode or non-meshcathode). The hole carrier layer can be formed of, for example,polythiophenes, polyanilines, and/or polyvinylcarbazoles, or polyions ofone or more of these polymers.

[0018] In some embodiments, the hole carrier layer is in contact with asubstrate that supports that cathode.

[0019] In certain embodiments, the photovoltaic cell further includes anadhesive material between the substrate that supports the cathode andthe hole carrier layer. In general, an adhesive material can adherematerial layers in contact with the adhesive during standard operatingconditions of a photovoltaic cell. In some embodiments, an adhesiveincludes one or more thermoplastics, thermosets, or pressure sensitiveadhesives.

[0020] In some embodiments, the photovoltaic cell or photovoltaic systemis electrically connected to an external load.

[0021] Embodiments can provide one or more of the following advantages.

[0022] In some embodiments, a mesh electrode can provide good electricalconductivity because it is formed of an electrically conductive material(as opposed to a semiconductor material), while at the same time havinga structure (e.g., a mesh structure) that allows a sufficient amount oflight therethrough so that the photovoltaic cell is more efficient atconverting light into electrical energy.

[0023] In certain embodiments, a mesh electrode can be sufficientlyflexible to allow the mesh electrode to be incorporated in thephotovoltaic cell using a continuous, roll-to-roll manufacturingprocess, thereby allowing manufacture of the photovoltaic cell atrelatively high throughput.

[0024] Using one or more mesh electrodes can reduce the cost and/orcomplexity associated with manufacturing a photovoltaic cell.

[0025] A photovoltaic cell having one or more mesh electrodes cantransfer energy in the form of light to energy in the form ofelectricity in a more efficient manner compared to certainsemiconductive electrodes.

[0026] Other features and advantages will be apparent from thedescription, drawings and from the claims.

DESCRIPTION OF DRAWINGS

[0027]FIG. 1 is a cross-sectional view of an embodiment of aphotovoltaic cell;

[0028]FIG. 2 is an elevational view of an embodiment of a meshelectrode;

[0029]FIG. 3 is a cross-sectional view of the mesh electrode of 2;

[0030]FIG. 4 is a cross-sectional view of a portion of a mesh electrode;

[0031]FIG. 5 is a cross-sectional view of another embodiment of aphotovoltaic cell;

[0032]FIG. 6 is a schematic of a system containing multiple photovoltaiccells electrically connected in series; and

[0033]FIG. 7 is a schematic of a system containing multiple photovoltaiccells electrically connected in parallel.

DETAILED DESCRIPTION

[0034]FIG. 1 shows a cross-sectional view of a photovoltaic cell 100that includes a transparent substrate 110, a mesh cathode 120, a holecarrier layer 130, a photoactive layer (containing an electron acceptormaterial and an electron donor material) 140, a hole blocking layer 150,an anode 160, and a substrate 170.

[0035] In general, during use, light impinges on the surface ofsubstrate 110, and passes through substrate 110, the openings in cathode120 and hole carrier layer 130. The light then interacts withphotoactive layer 140, causing electrons to be transferred from theelectron donor material in layer 140 to the electron acceptor materialin layer 140. The electron acceptor material then transmits theelectrons through hole blocking layer 150 to anode 160, and the electrondonor material transfers holes through hole carrier layer 130 to meshcathode 120. Anode 160 and mesh cathode 120 are in electrical connectionvia an external load so that electrons pass from anode 160, through theload, and to cathode 120.

[0036] As shown in FIGS. 2 and 3, mesh cathode 120 includes solidregions 122 and open regions 124. In general, regions 122 are formed ofelectrically conducting material so that mesh cathode 120 can allowlight to pass therethrough via regions 124 and conduct electrons viaregions 122.

[0037] The area of mesh cathode 120 occupied by open regions 124 (theopen area of mesh cathode 120) can be selected as desired. Generally,the open area of mesh cathode 120 is at least about 10% (e.g., at leastabout 20%, at least about 30%, at least about 40%, at least about 50%,at least about 60%, at least about 70%, at least about 80%) and/or atmost about 99% (e.g., at most about 95%, at most about 90%, at mostabout 85%) of the total area of mesh cathode 120.

[0038] Mesh cathode 120 can be prepared in various ways. In someembodiments, mesh cathode 120 is a woven mesh formed by weaving wires ofmaterial that form solid regions 122. The wires can be woven using, forexample, a plain weave, a Dutch, weave, a twill weave, a Dutch twillweave, or combinations thereof. In certain embodiments, mesh cathode 120is formed of a welded wire mesh. In some embodiments, mesh cathode 120is an expanded mesh formed. An expanded metal mesh can be prepared, forexample, by removing regions 124 (e.g., via laser removal, via chemicaletching, via puncturing) from a sheet of material (e.g., an electricallyconductive material, such as a metal), followed by stretching the sheet(e.g., stretching the sheet in two dimensions). In certain embodiments,mesh cathode 120 is a metal sheet formed by removing regions 124 (e.g.,via laser removal, via chemical etching, via puncturing) withoutsubsequently stretching the sheet.

[0039] In certain embodiments, solid regions 122 are formed entirely ofan electrically conductive material (e.g., regions 122 are formed of asubstantially homogeneous material that is electrically conductive).Examples of electrically conductive materials that can be used inregions 122 include electrically conductive metals, electricallyconductive alloys and electrically conductive polymers. Exemplaryelectrically conductive metals include gold, silver, copper, nickel,palladium, platinum and titanium. Exemplary electrically conductivealloys include stainless steel (e.g., 332 stainless steel, 316 stainlesssteel), alloys of gold, alloys of silver, alloys of copper, alloys ofnickel, alloys of palladium, alloys of platinum and alloys of titanium.Exemplary electrically conducting polymers include polythiophenes (e.g.,poly(3,4-ethelynedioxythiophene) (PEDOT)), polyanilines (e.g., dopedpolyanilines), polypyrroles (e.g., doped polypyrroles). In someembodiments, combinations of electrically conductive materials are used.

[0040] As shown in FIG. 4, in some embodiments, solid regions 122 areformed of a material 302 that is coated with a different material 304(e.g., using metallization, using vapor deposition). In general,material 302 can be formed of any desired material (e.g., anelectrically insulative material, an electrically conductive material,or a semiconductive material), and material 304 is an electricallyconductive material. Examples of electrically insulative material fromwhich material 302 can be formed include textiles, optical fibermaterials, polymeric materials (e.g., a nylon) and natural materials(e.g., flax, cotton, wool, silk). Examples of electrically conductivematerials from which material 302 can be formed include the electricallyconductive materials disclosed above. Examples of semiconductivematerials from which material 302 can be formed include indium tinoxide, fluorinated tin oxide, tin oxide and zinc oxide. In someembodiments, material 302 is in the form of a fiber, and material 304 isan electrically conductive material that is coated on material 302. Incertain embodiments, material 302 is in the form of a mesh (seediscussion above) that, after being formed into a mesh, is coated withmaterial 304. As an example, material 302 can be an expanded metal mesh,and material 304 can be PEDOT that is coated on the expanded metal mesh.

[0041] Generally, the maximum thickness of mesh cathode 120 (i.e., themaximum thickness of mesh cathode 120 in a direction substantiallyperpendicular to the surface of substrate 110 in contact with meshcathode 120) should be less than the total thickness of hole carrierlayer 130. Typically, the maximum thickness of mesh cathode 120 is atleast 0.1 micron (e.g., at least about 0.2 micron, at least about 0.3micron, at least about 0.4 micron, at least about 0.5 micron, at leastabout 0.6 micron, at least about 0.7 micron, at least about 0.8 micron,at least about 0.9 micron, bat least about one micron) and/or at mostabout 10 microns (e.g., at most about nine microns, at most about eightmicrons, at most about seven microns, at most about six microns, at mostabout five microns, at most about four microns, at most about threemicrons, at most about two microns).

[0042] While shown in FIG. 2 as having a rectangular shape, open regions124 can generally have any desired shape (e.g., square, circle,semicircle, triangle, diamond, ellipse, trapezoid, irregular shape). Insome embodiments, different open regions 124 in mesh cathode 120 canhave different shapes.

[0043] Although shown in FIG. 3 as having square cross-sectional shape,solid regions 122 can generally have any desired shape (e.g., rectangle,circle, semicircle, triangle, diamond, ellipse, trapezoid, irregularshape). In some embodiments, different solid regions 122 in mesh cathode120 can have different shapes.

[0044] In some embodiments, mesh cathode 120 is flexible (e.g.,sufficiently flexible to be incorporated in photovoltaic cell 100 usinga continuous, roll-to-roll manufacturing process). In certainembodiments, mesh cathode 120 is semi-rigid or inflexible. In someembodiments, different regions of mesh cathode 120 can be flexible,semi-rigid or inflexible (e.g., one or more regions flexible and one ormore different regions semi-rigid, one or more regions flexible and oneor more different regions inflexible).

[0045] Substrate 110 is generally formed of a transparent material. Asreferred to herein, a transparent material is a material which, at thethickness used in a photovoltaic cell 100, transmits at least about 60%(e.g., at least about 70%, at least about 75%, at least about 80%, atleast about 85%) of incident light at a wavelength or a range ofwavelengths used during operation of the photovoltaic cell. Exemplarymaterials from which substrate 110 can be formed include polyethyleneterephthalates, polyimides, polyethylene naphthalates, polymerichydrocarbons, cellulosic polymers, polycarbonates, polyamides,polyethers and polyether ketones. In certain embodiments, the polymercan be a fluorinated polymer. In some embodiments, combinations ofpolymeric materials are used. In certain embodiments, different regionsof substrate 110 can be formed of different materials.

[0046] In general, substrate 110 can be flexible, semi-rigid or rigid(e.g., glass). In some embodiments, substrate 110 has a flexural modulusof less than about 5,000 megaPascals. In certain embodiments, differentregions of substrate 110 can be flexible, semi-rigid or inflexible(e.g., one or more regions flexible and one or more different regionssemi-rigid, one or more regions flexible and one or more differentregions inflexible).

[0047] Typically, substrate 110 is at least about one micron (e.g., atleast about five microns, at least about 10 microns) thick and/or atmost about 1,000 microns (e.g., at most about 500 microns thick, at mostabout 300 microns thick, at most about 200 microns thick, at most about100 microns, at most about 50 microns) thick.

[0048] Generally, substrate 110 can be colored or non-colored. In someembodiments, one or more portions of substrate 110 is/are colored whileone or more different portions of substrate 110 is/are non-colored.

[0049] Substrate 110 can have one planar surface (e.g., the surface onwhich light impinges), two planar surfaces (e.g., the surface on whichlight impinges and the opposite surface), or no planar surfaces. Anon-planar surface of substrate 110 can, for example, be curved orstepped. In some embodiments, a non-planar surface of substrate 110 ispatterned (e.g., having patterned steps to form a Fresnel lens, alenticular lens or a lenticular prism).

[0050] Hole carrier layer 130 is generally formed of a material that, atthe thickness used in photovoltaic cell 100, transports holes to meshcathode 120 and substantially blocks the transport of electrons to meshcathode 120. Examples of materials from which layer 130 can be formedinclude polythiophenes (e.g., PEDOT), polyanilines, polyvinylcarbazoles,polyphenylenes, polyphenylvinylenes, polysilanes,polythienylenevinylenes and/or polyisothianaphthanenes. In someembodiments, hole carrier layer 130 can include combinations of holecarrier materials.

[0051] In general, the distance between the upper surface of holecarrier layer 130 (i.e., the surface of hole carrier layer 130 incontact with active layer 140) and the upper surface of substrate 110(i.e., the surface of substrate 110 in contact with mesh electrode 120)can be varied as desired. Typically, the distance between the uppersurface of hole carrier layer 130 and the upper surface of mesh cathode120 is at least 0.01 micron (e.g., at least about 0.05 micron, at leastabout 0.1 micron, at least about 0.2 micron, at least about 0.3 micron,at least about 0.5 micron) and/or at most about five microns (e.g., atmost about three microns, at most about two microns, at most about onemicron). In some embodiments, the distance between the upper surface ofhole carrier layer 130 and the upper surface of mesh cathode 120 is fromabout 0.01 micron to about 0.5 micron.

[0052] Active layer 140 generally contains an electron acceptor materialand an electron donor material.

[0053] Examples of electron acceptor materials include formed offullerenes, oxadiazoles, carbon nanorods, discotic liquid crystals,inorganic nanoparticles (e.g., nanoparticles formed of zinc oxide,tungsten oxide, indium phosphide, cadmium selenide and/or leadsulphide), inorganic nanorods (e.g., nanorods formed of zinc oxide,tungsten oxide, indium phosphide, cadmium selenide and/or leadsulphide), or polymers containing moieties capable of acceptingelectrons or forming stable anions (e.g., polymers containing CN groups,polymers containing CF₃ groups). In some embodiments, the electronacceptor material is a substituted fullerene (e.g., PCBM). In someembodiments, active layer 140 can include a combination of electronacceptor materials.

[0054] Examples of electron donor materials include discotic liquidcrystals, polythiophenes, polyphenylenes, polyphenylvinylenes,polysilanes, polythienylvinylenes, and polyisothianaphthalenes. In someembodiments, the electron donor material is poly(3-hexylthiophene). Incertain embodiments, active layer 140 can include a combination ofelectron donor materials.

[0055] Generally, active layer 140 is sufficiently thick to berelatively efficient at absorbing photons impinging thereon to formcorresponding electrons and holes, and sufficiently thin to berelatively efficient at transporting the holes and electrons to layers130 and 150, respectively. In certain embodiments, layer 140 is at least0.05 micron (e.g., at least about 0.1 micron, at least about 0.2 micron,at least about 0.3 micron) thick and/or at most about one micron (e.g.,at most about 0.5 micron, at most about 0.4 micron) thick. In someembodiments, layer 140 is from about 0.1 micron to about 0.2 micronthick.

[0056] Hole blocking layer 150 is general formed of a material that, atthe thickness used in photovoltaic cell 100, transports electrons toanode 160 and substantially blocks the transport of holes to anode 160.Examples of materials from which layer 150 can be formed include LiF andmetal oxides (e.g., zinc oxide, titanium oxide).

[0057] Typically, hole blocking layer 150 is at least 0.02 micron (e.g.,at least about 0.03 micron, at least about 0.04 micron, at least about0.05 micron) thick and/or at most about 0.5 micron (e.g., at most about0.4 micron, at most about 0.3 micron, at most about 0.2 micron, at mostabout 0.1 micron) thick.

[0058] Anode 160 is generally formed of an electrically conductivematerial, such as one or more of the electrically conductive materialsnoted above. In some embodiments, anode 160 is formed of a combinationof electrically conductive materials.

[0059] Substrate 170 can be formed of a transparent material or anon-transparent material. For example, in embodiments in whichphotovoltaic cell uses light that passes through anode 160 during use,substrate 170 is desirably formed of a transparent material.

[0060] Exemplary materials from which substrate 170 can be formedinclude polyethylene terephthalates, polyimides, polyethylenenaphthalates, polymeric hydrocarbons, cellulosic polymers,polycarbonates, polyamides, polyethers and polyether ketones. In certainembodiments, the polymer can be a fluorinated polymer. In someembodiments, combinations of polymeric materials are used. In certainembodiments, different regions of substrate 110 can be formed ofdifferent materials.

[0061] In general, substrate 170 can be flexible, semi-rigid or rigid.In some embodiments, substrate 170 has a flexural modulus of less thanabout 5,000 megaPascals. In certain embodiments, different regions ofsubstrate 170 can be flexible, semi-rigid or inflexible (e.g., one ormore regions flexible and one or more different regions semi-rigid, oneor more regions flexible and one or more different regions inflexible).Generally, substrate 170 is substantially non-scattering.

[0062] Typically, substrate 170 is at least about one micron (e.g., atleast about five microns, at least about 10 microns) thick and/or atmost about 200 microns (e.g., at most about 100 microns, at most about50 microns) thick.

[0063] Generally, substrate 170 can be colored or non-colored. In someembodiments, one or more portions of substrate 170 is/are colored whileone or more different portions of substrate 170 is/are non-colored.

[0064] Substrate 170 can have one planar surface (e.g., the surface ofsubstrate 170 on which light impinges in embodiments in which during usephotovoltaic cell 100 uses light that passes through anode 160), twoplanar surfaces (e.g., the surface of substrate 170 on which lightimpinges in embodiments in which during use photovoltaic cell 100 useslight that passes through anode 160 and the opposite surface ofsubstrate 170), or no planar surfaces. A non-planar surface of substrate170 can, for example, be curved or stepped. In some embodiments, anon-planar surface of substrate 170 is patterned (e.g., having patternedsteps to form a Fresnel lens, a lenticular lens or a lenticular prism).

[0065]FIG. 5 shows a cross-sectional view of a photovoltaic cell 400that includes an adhesive layer 410 between substrate 110 and holecarrier layer 130.

[0066] Generally, any material capable of holding mesh cathode 130 inplace can be used in adhesive layer 410. In general, adhesive layer 410is formed of a material that is transparent at the thickness used inphotovoltaic cell 400. Examples of adhesives include epoxies andurethanes. Examples of commercially available materials that can be usedin adhesive layer 410 include Bynel™ adhesive (DuPont) and 615 adhesive(3M). In some embodiments, layer 410 can include a fluorinated adhesive.In certain embodiments, layer 410 contains an electrically conductiveadhesive. An electrically conductive adhesive can be formed of, forexample, an inherently electrically conductive polymer, such as theelectrically conductive polymers disclosed above (e.g., PEDOT). Anelectrically conductive adhesive can be also formed of a polymer (e.g.,a polymer that is not inherently electrically conductive) that containsone or more electrically conductive materials (e.g., electricallyconductive particles). In some embodiments, layer 410 contains aninherently electrically conductive polymer that contains one or moreelectrically conductive materials.

[0067] In some embodiments, the thickness of layer 410 (i.e., thethickness of layer 410 in a direction substantially perpendicular to thesurface of substrate 110 in contact with layer 410) is less thick thanthe maximum thickness of mesh cathode 120. In some embodiments, thethickness of layer 410 is at most about 90% (e.g., at most about 80%, atmost about 70%, at most about 60%, at most about 50%, at most about 40%,at most about 30%, at most about 20%) of the maximum thickness of meshcathode 120. In certain embodiments, however, the thickness of layer 410is about the same as, or greater than, the maximum thickness of meshcathode 130.

[0068] In general, a photovoltaic cell having a mesh cathode can bemanufactured as desired.

[0069] In some embodiments, a photovoltaic cell can be prepared asfollows. Electrode 160 is formed on substrate 170 using conventionaltechniques, and hole-blocking layer 150 is formed on electrode 160(e.g., using a vacuum deposition process or a solution coating process).Active layer 140 is formed on hole-blocking layer 150 (e.g., using asolution coating process, such as slot coating, spin coating or gravurecoating). Hole carrier layer 130 is formed on active layer 140 (e.g.,using a solution coating process, such as slot coating, spin coating orgravure coating). Mesh cathode 120 is partially disposed in hole carrierlayer 130 (e.g., by disposing mesh cathode 120 on the surface of holecarrier layer 130, and pressing mesh cathode 120). Substrate 110 is thenformed on mesh cathode 120 and hole carrier layer 130 using conventionalmethods.

[0070] In certain embodiments, a photovoltaic cell can be prepared asfollows. Electrode 160 is formed on substrate 170 using conventionaltechniques, and hole-blocking layer 150 is formed on electrode 160(e.g., using a vacuum deposition or a solution coating process). Activelayer 140 is formed on hole-blocking layer 150 (e.g., using a solutioncoating process, such as slot coating, spin coating or gravure coating).Hole carrier layer 130 is formed on active layer 140 (e.g., using asolution coating process, such as slot coating, spin coating or gravurecoating). Adhesive layer 410 is disposed on hole carrier layer 130 usingconventional methods. Mesh cathode 120 is partially disposed in adhesivelayer 410 and hole carrier layer 130 (e.g., by disposing mesh cathode120 on the surface of adhesive layer 410, and pressing mesh cathode120). Substrate 110 is then formed on mesh cathode 120 and adhesivelayer 410 using conventional methods.

[0071] While the foregoing processes involve partially disposing meshcathode 120 in hole carrier layer 130, in some embodiments, mesh cathode120 is formed by printing the cathode material on the surface of carrierlayer 130 or adhesive layer 410 to provide an electrode having the openstructure shown in the figures. For example, mesh cathode 120 can beprinted using an inkjet printer, a screen printer, or gravure printer.The cathode material can be disposed in a paste which solidifies uponheating or radiation (e.g., UV radiation, visible radiation, IRradiation, electron beam radiation). The cathode material can be, forexample, vacuum deposited in a mesh pattern through a screen or afterdeposition it may be patterned by photolithography.

[0072] Multiple photovoltaic cells can be electrically connected to forma photovoltaic system. As an example, FIG. 6 is a schematic of aphotovoltaic system 500 having a module 510 containing photovoltaiccells 520. Cells 520 are electrically connected in series, and system500 is electrically connected to a load. As another example, FIG. 7 is aschematic of a photovoltaic system 600 having a module 610 that containsphotovoltaic cells 620. Cells 620 are electrically connected inparallel, and system 600 is electrically connected to a load. In someembodiments, some (e.g., all) of the photovoltaic cells in aphotovoltaic system can have one or more common substrates. In certainembodiments, some photovoltaic cells in a photovoltaic system areelectrically connected in series, and some of the photovoltaic cells inthe photovoltaic system are electrically connected in parallel.

[0073] While certain embodiments have been disclosed, other embodimentsare also possible.

[0074] As another example, while cathodes formed of mesh have beendescribed, in some embodiments a mesh anode can be used. This can bedesirable, for example, when light transmitted by the anode is used. Incertain embodiments, both a mesh cathode and a mesh anode are used. Thiscan be desirable, for example, when light transmitted by both thecathode and the anode is used.

[0075] As an example, while embodiments have generally been described inwhich light that is transmitted via the cathode side of the cell isused, in certain embodiments light transmitted by the anode side of thecell is used (e.g., when a mesh anode is used). In some embodiments,light transmitted by both the cathode and anode sides of the cell isused (when a mesh cathode and a mesh anode are used).

[0076] As a further example, while electrodes (e.g., mesh electrodes,non-mesh electrodes) have been described as being formed of electricallyconductive materials, in some embodiments a photovoltaic cell mayinclude one or more electrodes (e.g., one or more mesh electrodes, oneor more non-mesh electrodes) formed of a semiconductive material.Examples of semiconductive materials include indium tin oxide,fluorinated tin oxide, tin oxide and zinc oxide.

[0077] As an additional example, in some embodiments, one or moresemiconductive materials can be disposed in the open regions of a meshelectrode (e.g., in the open regions of a mesh cathode, in the openregions of a mesh anode, in the open regions of a mesh cathode and theopen regions of a mesh anode). Examples of semiconductive materialsinclude tin oxide, fluorinated tin oxide, tin oxide and zinc oxide.Typically, the semiconductive material disposed in an open region of amesh electrode is transparent at the thickness used in the photovoltaiccell.

[0078] As another example, in certain embodiments, a protective layercan be applied to one or both of the substrates. A protective layer canbe used to, for example, keep contaminants (e.g., dirt, water, oxygen,chemicals) out of a photovoltaic cell and/or to ruggedize the cell. Incertain embodiments, a protective layer can be formed of a polymer(e.g., a fluorinated polymer).

[0079] As a further example, while certain types of photovoltaic cellshave been described that have one or more mesh electrodes, one or moremesh electrodes (mesh cathode, mesh anode, mesh cathode and mesh anode)can be used in other types of photovoltaic cells as well. Examples ofsuch photovoltaic cells include photoactive cells with an activematerial formed of amorphous silicon, cadmium selenide, cadmiumtelluride, copper indium sulfide, and copper indium gallium arsenide.

[0080] As an additional example, while described as being formed ofdifferent materials, in some embodiments materials 302 and 304 areformed of the same material.

[0081] As another example, although shown in FIG. 4 as being formed ofone material coated on a different material, in some embodiments solidregions 122 can be formed of more than two coated materials (e.g., threecoated materials, four coated materials, five coated materials, sixcoated materials.

[0082] Other embodiments are in the claims.

What is claimed is:
 1. A photovoltaic cell, comprising: a firstelectrode; a mesh electrode; and an active layer between the first andmesh electrodes, the active layer comprising: an electron acceptormaterial; and an electron donor material.
 2. The photovoltaic cell ofclaim 1, wherein the mesh electrode is a cathode.
 3. The photovoltaiccell of claim 1, wherein the mesh electrode is an anode.
 4. Thephotovoltaic cell of claim 1, wherein the mesh comprises an electricallyconductive material.
 5. The photovoltaic cell of claim 4, wherein theelectrically conductive material is selected from the group consistingof metals, alloys, polymers and combinations thereof.
 6. Thephotovoltaic cell of claim 1, wherein the mesh electrode compriseswires.
 7. The photovoltaic cell of claim 6, wherein the wires comprisean electrically conductive material.
 8. The photovoltaic cell of claim7, wherein the electrically conductive material is selected from thegroup consisting of metals, alloys, polymers and combinations thereof.9. The photovoltaic cell of claim 6, wherein the wires comprise acoating including an electrically conductive material.
 10. Thephotovoltaic cell of claim 9, wherein the electrically conductivematerial is selected from the group consisting of metals, alloys,polymers and combinations thereof.
 11. The photovoltaic cell of claim 1,wherein the mesh electrode comprises an expanded mesh.
 12. Thephotovoltaic cell of claim 1, wherein the mesh electrode comprises awoven mesh.
 13. The photovoltaic cell of claim 1, wherein the electronacceptor material comprises a material selected from the groupconsisting of fullerenes, inorganic nanoparticles, oxadiazoles, discoticliquid crystals, carbon nanorods, inorganic nanorods, polymerscontaining CN groups, polymers containing CF₃ groups and combinationsthereof.
 14. The photovoltaic cell of claim 1, wherein the electronacceptor material comprises a substituted fullerene.
 15. Thephotovoltaic cell of claim 1, wherein the electron donor materialcomprises a material selected from the group consisting of discoticliquid crystals, polythiophenes, polyphenylenes, polyphenylvinylenes,polysilanes, polythienylvinylenes and polyisothianaphthalenes.
 16. Thephotovoltaic cell of claim 1, wherein the electron donor materialcomprises poly(3-hexylthiophene).
 17. The photovoltaic cell of claim 1,further comprising a hole blocking layer between the active layer andthe first electrode.
 18. The photovoltaic cell of claim 17, wherein thehole blocking layer comprises a material selected from the groupconsisting of LiF, metal oxides and combinations thereof.
 19. Thephotovoltaic cell of claim 1, further comprising a hole blocking layerbetween the active layer and the mesh electrode.
 20. The photovoltaiccell of claim 19, wherein the hole blocking layer comprises a materialselected from the group consisting of LiF, metal oxides and combinationsthereof.
 21. The photovoltaic cell of claim 1, further comprising a holecarrier layer between the active layer and the mesh electrode.
 22. Thephotovoltaic cell of claim 21, wherein the hole carrier layer comprisesa material selected from the group consisting of polythiophenes,polyanilines, polyvinylcarbazoles, polyphenylenes, polyphenylvinylenes,polysilanes, polythienylenevinylenes, polyisothianaphthanenes andcombinations thereof.
 23. The photovoltaic cell of claim 1, furthercomprising a hole carrier layer between the active layer and the firstelectrode.
 24. The photovoltaic cell of claim 23, wherein the holecarrier layer comprises a material selected from the group consisting ofpolythiophenes, polyanilines, polyvinylcarbazoles, polyphenylenes,polyphenylvinylenes, polysilanes, polythienylenevinylenes,polyisothianaphthanenes and combinations thereof.
 25. The photovoltaiccell of claim 1, wherein the first electrode comprises a mesh electrode.26. A photovoltaic cell, comprising: a first electrode; a meshelectrode; an active layer between the first and mesh electrodes, theactive layer comprising: an electron acceptor material; and an electrondonor material; a hole blocking layer between the first electrode andthe active layer; and a hole carrier layer between the mesh electrodeand the active layer.
 27. The photovoltaic cell of claim 26, wherein themesh comprises an electrically conductive material.
 28. The photovoltaiccell of claim 27, wherein the electrically conductive material isselected from the group consisting of metals, alloys, polymers andcombinations thereof.
 29. The photovoltaic cell of claim 26, wherein thehole carrier layer comprises a material selected from the groupconsisting of polythiophenes, polyanilines, polyvinylcarbazoles,polyphenylenes, polyphenylvinylenes, polysilanes,polythienylenevinylenes, polyisothianaphthanenes and combinationsthereof.
 30. The photovoltaic cell of claim 29, wherein the holeblocking layer comprises a material selected from the group consistingof LiF, metal oxides and combinations thereof.
 31. The photovoltaic cellof claim 26, wherein the hole blocking layer comprises a materialselected from the group consisting of LiF, metal oxides and combinationsthereof.
 32. The photovoltaic cell of claim 26, wherein the meshelectrode comprises wires.
 33. The photovoltaic cell of claim 32,wherein the wires comprise an electrically conductive material.
 34. Thephotovoltaic cell of claim 33, wherein the electrically conductivematerial is selected from the group consisting of metals, alloys,polymers and combinations thereof.
 35. The photovoltaic cell of claim32, wherein the wires comprise a coating including an electricallyconductive material.
 36. The photovoltaic cell of claim 35, wherein theelectrically conductive material is selected from the group consistingof metals, alloys, polymers and combinations thereof.
 37. Thephotovoltaic cell of claim 26, wherein the mesh electrode comprises anexpanded mesh.
 38. The photovoltaic cell of claim 26, wherein the meshelectrode comprises a woven mesh.
 39. The photovoltaic cell of claim 26,wherein the first electrode comprises a mesh electrode.
 40. Thephotovoltaic cell of claim 26, further comprising a substrate supportingthe mesh electrode.
 41. The photovoltaic cell of claim 40, furthercomprising an adhesive material between the substrate and the holecarrier layer.
 42. The photovoltaic cell of claim 40, wherein the holecarrier layer is in contact with the substrate.
 43. A photovoltaicsystem comprising a plurality of photovoltaic cells of claim 1, at leastsome of the plurality of photovoltaic cells being electricallyconnected.
 44. The photovoltaic system of claim 43, wherein all of theplurality of photovoltaic cells are electrically connected.
 45. Thephotovoltaic system of claim 43, wherein at least some of theelectrically connected photovoltaic cells are electrically connected inparallel.
 46. The photovoltaic system of claim 43, wherein at least someof the electrically connected photovoltaic cells are electricallyconnected in series.
 47. The photovoltaic system of claim 43, whereinthe photovoltaic system is wherein at least some of the electricallyconnected photovoltaic cells are electrically connected in to a load.48. A photovoltaic system comprising a plurality of photovoltaic cellsof claim 24, at least some of the plurality of photovoltaic cells beingwherein at least some of the electrically connected photovoltaic cellsare electrically connected.
 49. The photovoltaic system of claim 48,wherein all of the plurality of photovoltaic cells are electricallyconnected.
 50. The photovoltaic system of claim 48, wherein at leastsome of the electrically connected photovoltaic cells are electricallyconnected in parallel.
 51. The photovoltaic system of claim 48, whereinat least some of the electrically connected photovoltaic cells areelectrically connected in series.
 52. The photovoltaic system of claim48, wherein the photovoltaic system is wherein at least some of theelectrically connected photovoltaic cells are electrically connected inparallel to a load.